VC21LPFilter

V = Variables

C = Claculation functions

The VC21LPFilter function implements a low-pass digital filter of the first order for values in the range from -999999 to +999999. It ' also provided the pre-charge filter option.

IMPLEMENTATION

VC20LPFilter (Mode, Tsample, Tau, FilterIn, FilterOut)

Parameters:

IN/OUT	VARIABLE TYPE	EXAMPLE NAME	DIM
IN	CONST / GLOBAL	Mode	F	Mode of operation (0=pre-charge, 1=filter execution).
IN	CONST / SYSTEM	Tsample	W	Sample time filter (msec) [0÷32767].
IN	CONST / SYSTEM	Tau	W	The filter time constant (ms) [0÷32767]
IN	GLOBAL	FilterIn	L	Value of the variable that you want to filter [-999999÷999999]
OUT	GLOBAL	FilterOut	L	Value of the filtered variable [-999999÷999999]

Description

The VC21LPFilter function implements a digital low-pass filter of the first order whose time constant (Tau) is defined in the parameters passed to the function. Assuming you start from a zero input variable value, the output of the filter takes a value equal to 63% of the input after the long Tau. Similarly the cutoff frequency of the filter is . If the Mode topic is zero allows you to preload the filter to a value that can be set with the topic FilterIn.

Esempio

;---------------------------------------------
; Project           : REG_012
; Module Name  : ReadTemp
; Author            : 
; Description     : Read temperature & filter
;---------------------------------------------
MAIN:
	CALL ReadTemp
	swTsample = 100		;100 ms tempo campionamento filtro
        swTau = 5000		;5 sec costante di tempo filtro
        gfMode = 1		; normale esecuzione
	VC21LPFilter (gfMode,swTsample, swTau, gwFilterIn, gwFilterOut)
 
        WAIT 1
    	JUMP MAIN

Note

La funzione contiene all'interno un timer per eseguire effettivamente il filtro ogni Tempo di campionamento (Tsample). La funzione deve essere quindi eseguita ad una frequenza superiore rispetto al Tempo di campionamento (Tsample), in genere ad ogni ciclo task.